The modern production technology involves a range of auxiliary materials including petroleum, vegetable and animal oils, pastes, conservants, lubricating and cooling liquids, etc. They tend to remain at the surface of the workpieces and necessitate cleaning prior to assembly operations or application of protective coatings. Used as cleaning agents are hydrocarbon solvents, chlor- and/or fluorine-containing hydrocarbon solvents, aqueous solutions of electrolytes, surface-active substances, and compounds based thereon. After cleaning these substances carrying impurities are discharged to the outside in the form of industrial sewage, vapours, combusted still residues, and slime. The cost of the thus irrevocably lost chemical substances and the damage to the environment are enormously high.
There is known a method of cleaning workpieces (cf., SU, A, 1,093,732) which includes treating the surface of workpieces with aqueous solutions containing surface-active substances and activating agents, such as ammonium perfulfate, monoethanolamine phosphate, sulfamic acid, oxalic acid, naphthalene sulfonates, and water. The used solutions are regenerated by settling, removing petroleum products floated to the surface of the solution, and filtering the mechanical impurities.
In this method regeneration of the used solution resides only in settling and filtering nonhomogeneous systems. The used solvent contaminated with soluble impurities is not regenerated. Therefore, aqueous solutions, organic solvents and petroleum products are discharged to the outside.
There is also known a method of cleaning the surface of workpieces from petroleum products and mechanical impurities (cf., SU, A, 541,857) residing in that the workpieces to be cleaned are preliminarily heated to 60.degree. C., and washed with a composition containing white spirit, hydroxyethylated alkylphenols or fatty alcohol, water, sodium alkylsulfonate and diesel fuel. Therewith, the workpiece is held at a temperature 50.degree.-60.degree. C. for 10-15 minutes and thereafter washed with an aqueous solution heated to 60.degree. C. and containing 0.1-3.0% tripolyphosphate and 0.1-1% hydroxyethylated alkylphenols. Regeneration of the used solution is carried out by heating it to 80.degree.-90.degree. C., after which the floating petroleum product is separated, and the aqueous solution of the washing composition is repeatedly used for successive cleaning procedures.
However, in the course of cleaning workpieces the solvent tends to partially react with the washed impurities. Petroleum products, fats and solid mechanical impurities periodically released from the process contain the solvent and substances resulting from chemical reaction thereof with impurities, and therefore are subject to concealment.
The aqueous phase saturated with soluble ingredients of the petroleum products is also concealed.
There is further known a method of cleaning the surface of workpieces contaminated with compositions of organic matter (cf;, SU, A,957,672). The method includes treating the workpiece surfaces with polyfluorinated ethers or volatile chlor- and/or fluorine-containing alkanes with admixture of perfluoroalcohols, perfluoroethers, perfluoracids in an amount of 0.02-1 mass percent. Volatile solvents act to spread the dissolved substance at the surface and, while evaporating at a fast rate, remove (disperse) the film of petroleum product from the surface. The amount of the composition consumed is several cu. cm per 100 square inches of surface area. This known method fails to solve the problem of separating the used solutions into initial ingredients for reuse, whereas the consumption of washing compositions is high; the volatile base, viz., fluorohydrocarbon liquids evaporate and break the ozone layer of the atmosphere.
There is known a method of cleaning the surface of workpieces (cf., GB, A, 2,104,104) in which the surface is cleaned with a circulating solvent containing liquid chlor-containing hydrocarbon and a surface-active agent having ingredients thereof so preselected as not to allow them to mix or enter into reaction with process impurities. The used solution is regenerated by evaporating the liquid chlor-containing hydrocarbon. After condensation the surface-active agent is added to the cleaned solvent, and the workpieces are conveyed for repeated cleaning. After evaporation of the solvent the washed off impurities are separated from the surface-active agent to ensure that the latter can be reused. This process is not materialized in the prior art method, whereas the method per se can be used within a narrow range of applications, particularly for cleaning the surface of workpieces after the application of protective coatings thereto possibly accompanied by a tendency of the chlor-containing solvent to decompose in the presence of water and metal chlorides leading to the formation of highly toxic substances.
The known methods can be carried out by a turret type apparatus for cleaning the surface of workpieces made up of standard parts and units depending on the type of the washing solution or demands imposed by the process (cf., Dr; W. Kampschulte, et al., West Germany, Zollingen "Apparatus for cleaning and decreasing using ultrasound and therewithout"). The apparatus comprises a cleaning chamber having a mechanical and an ultrasonic cleaning activation means, a distillation arrangement, a means for separating solid mechanical impurities, and condensers for capturing and condensing vapours of the solvent. This apparatus is characterized by insufficient degree of utilization of the solvent due to the decomposition and reaction of the solvent with the impurities being washed off and with water, and due to the need for concealment of still residues containing substantial quantities of the solvent after the distillation. Losses of solvent in apparatus of this type may amount to between 0.1 and 0.5 kg per 1 m.sup.2 of the cleaned workpiece surface.
There is known a method of cleaning workpieces from petroleum products and mechanical impurities carried out by an apparatus disclosed in SU, A, 1,189,515 comprising the steps of cleaning the surface of the workpieces with a circulating flow of solvent, drying the cleaned workpieces, regenerating the used solvent, and separating the washed off impurities. According to this method, the workpieces are heated to a preset temperature, and treated with the circulating solvent. Subsequent to cleaning the workpieces are dried in a vacuum. The dried workpieces are then cooled and withdrawn from the apparatus. Vapours of the solvent resulting from drying are condensed and returned to the cleaning cycle. The used solvent is regenerated by distillation resulting in a distillate and still residues containing a solvent that failed to evaporate, washed off petroleum products, and mechanical impurities. The distillate is returned to the cleaning cycle, whereas the liquid constituents of the still residues are filtered and utilized.
Inherent in this method are high losses of the solvent due to its high volatility, entrainment by the still residue, and the tendency thereof to enter into reaction with the impurities and water.
There is known an apparatus for carrying out the above method (cf., SU, A, 1,189,515) which comprises a conveyer for transporting the workpieces and a series of units including an inlet chamber, neutral chambers, a cleaning chamber with a system for circulating the solvent, a drying chamber connected to a vacuum generating system, a condenser for caputring the solvent vapours, a still, a distillate collector, a petroleum product collector, and a filter for separating mechanical impurities. All the chambers are hermetically sealed by gates.